The government of Ukraine has given Russia an ultimatum to free Ukrainian generals and admirals who are being held in Crimea. The warning came at a press briefing by government officials in Kyiv on Monday.

In the meantime, Ukraine’s national security and defense secretary said more than 10,000 personnel are being ordered to mobilize.

Ukrainian navy officers had been negotiating with the Russian side for an orderly withdrawal from the base but had not received orders from Kyiv.

Those orders came hours later when Ukraine called for all its remaining military in Crimea to withdraw to the mainland.

Navy officers Sunday had told Reuters TV they would defend the base to the end and that Russian military promised they would be allowed to leave with honor.

Ukraine Navy Captain Olexander Lantuhk said they did not want to turn over armaments and ships to the Russians. He said they do not see any reason why they should leave their vessels and weapons. As soldiers, they are responsible for them, he added.

The navy base was one of the few left in Crimea remaining under the Ukrainian flag.

Russian troops, local militia, and pro-Russia mobs this month surrounded and took over many of Ukraine's military bases in Crimea, seizing ships and weapons.

Russian troops Saturday stormed two Ukrainian naval bases in Sevastopol and Novofedorovka and took control of a submarine and flagship.

They used armored personnel carriers (APCs) to break down a wall and gate at Ukraine's largest military hold-out, Belbek Air Force base. One Ukrainian sailor was reported injured.

Ukrainian navy Lieutenant Anatoly Mozgovoi on Sunday at Feodosia acknowledged Russia was now in control.

When asked about the plan for the base, he responded "you can see what has happened with Crimea". Currently the situation is de-facto.

Ukraine's interim government has ordered its troops to withdraw from Crimea.

Kyiv said Monday it is pulling out its troops in response to the annexation of Crimea by Russia. Ukraine's acting president, Oleksandr Turchynov, said the defense ministry has been instructed to redeploy Ukrainian forces from the Black Sea peninsula. He said the move is a response to threats by Russian forces on the lives of Ukrainian service members and their families.

As Ukraine announced its troop evacuation Monday, Russian Defense Minister Sergei Shoigu visited Russia's military headquarters in Sevastopol, where he reviewed troops and met with the former head of Ukraine's navy, Rear Admiral Denis Berezovsky, who has switched allegiances and become a deputy commander of the Black Sea Fleet. Ukrainian authorities have charged him with treason.

Romania's concerns

Romania's President Traian Basescu on Monday said the North Atlantic Treaty Organization (NATO) must reposition its resources in the wake of Moscow's military operations in recent months, without offering specifics.

Romania, a former Communist state which joined the European Union in 2007, has been among the staunchest advocates of Western sanctions against Moscow, after Russia annexed the Ukrainian province of Crimea.

Romania is especially wary that its neighbor Moldova, a tiny state with a Russian-speaking minority, could be next in Moscow's sights.

Referendum

The aggressive moves follow a controversial March 16 referendum in Crimea that saw the vast majority there vote to become part of Russia. Moscow on Friday passed legislation making Crimea officially a part of the Russian Federation.

Ukraine, the European Union, and United States condemned the vote as an illegal and illegitimate land-grab. Moscow says its actions were necessary to protect ethnic Russians from alleged persecution by Kyiv's interim government, which it calls fascist and anti-Russian.

The tensions over Crimea are the worst between Russia and western nations since the end of the Cold War.

Western nations warned Russia against further moves on Eastern Ukraine where Simferpro-Russia populations are calling for similar referendums. Russian military has built up, and held recent drills, along the border with Ukraine raising concerns about further incursions.

Crimea's Prime Minister Sergei Aksyonov on Sunday called for Russians in Ukraine to fight against the pro-western government in Kyiv. In a televised speech and in Facebook and Twitter comments, he said Southeastern Ukraine's future was a close union with the Russian Federation.

Ukraine's Kremlin-leaning President Viktor Yanukovych fled Ukraine to Russia and was voted out of office after months of street protests in Kyiv turned violent.

The protests were sparked when Yanukovych abruptly pulled out of a trade deal with the European Union in favor of closer ties with Russia.

Crimea energy

Russian Prime Minister Dmitry Medvedev said on Monday international negotiations would be needed to secure supplies of energy and water to the region of Crimea.

“This issue needs to be decided through international negotiations,” Medvedev told a ministerial meeting, suggesting Russia may engage with Ukraine over the issue. “We need to choose the best way to supply the peninsula.”

Crimea receives around 80 percent of its electricity supplies, 85 percent of its water and a large part of gas from Ukraine, Medvedev said.

'Self-defense' forces

Crimean “self-defense” forces that helped Russia wrest the peninsula from Ukraine will be transformed into a national guard, a senior local security official said, arguing confidently that hostilities were over.

The militia, denounced by the Western-backed government in Kiev as Moscow-sponsored thugs, went hand in hand with Russian troops in recent days taking over military facilities in the region and raising the Russian tricolor.

Schearf is reporting from Sevastopol, Crimea, and Herman is reporting from Kyiv, Ukraine.